GENEVA (AP) — The World Health Organization says it is making progress in tracking new Ebola cases in eastern Congo but Doctors Without Borders asserts that the vast majority were not previously known as contacts of victims.

WHO emergencies chief Dr. Michael Ryan told reporters in Geneva on Tuesday that the number of new cases traced back to earlier patients is improving.

Doctors Without Borders, however, warned that those efforts are still failing.

The international aid organization said 80 percent of new confirmed Ebola virus cases were not already known as contacts.

The aid group said that is complicating efforts to understand how the deadly disease is spreading.

More than 1,200 people have now died in the second-deadliest Ebola outbreak in history. Rebel attacks and community resistance are challenging the virus containment efforts.